1. Field of Invention
The present invention relates to an axial fan which includes a plurality of blades arranged at a predetermined pitch about a rotation axis, and which takes in air in the direction of the rotation axis and discharges the air by rotating the plurality of the blades about the rotation axis. Further, the present invention relates to a centrifugal fan which includes a plurality of blades arranged at a predetermined pitch about a rotation axis, and which takes in air in the direction of the rotation axis and discharges air in a direction tangential to the rotation of the plurality of the blades by rotating the plurality of the blades about the rotation axis. The axial fan or the centrifugal fan may be used as an intake fan or an exhaust fan for electronic equipment such as a computer or projector.
2. Description of Related Art
Electronic equipment, such as a personal computer or a projector, conventionally employs an intake fan that cools the electronic equipment by taking in air from outside the electronic equipment and by having air impinge on the heat generating component, or an exhaust fan that outwardly discharges hot air from within the electronic equipment. As the intake fan or the exhaust fan, an axial fan and a centrifugal fan are available.
The axial fan has a plurality of fans arranged at a predetermined pitch around the rotation axis. By rotating the plurality of the blades about the rotation axis, air is taken in and discharged in the direction of the rotation axis.
The centrifugal fan has a plurality of fans arranged at a predetermined pitch around the rotation axis. By rotating the plurality of the blades on the rotation axis, air is taken in the direction of the rotation axis and discharged in a direction tangential to the rotation of the plurality of the blades.
Such an axial fan or centrifugal fan is arranged over a microprocessor unit forming a computer, or in the vicinity of a liquid-crystal display panel as an electro-optical device forming a projector or a lamp as a light source system in the projector. By having cooling air impinge on these heat generating components or discharging hot air out, efficient cooling is attained.
The axial fan installed in the electronic equipment conventionally employs five to eleven blades having the same shape and arranged about a rotation axis at a predetermined equal pitch.
The axial and centrifugal fans, provided with the blades having the same shape and arranged at the predetermined equal pitch, suffer from wind noise caused by the flow of air and a whirring sound unique to the fan. For instance, when an axial fan having nine blades arranged around a rotation axis at an equal pitch is rotated at a rotational speed of 4000 rpm, a whirring sound of 4000/60xc3x979 (Hz) is generated. Since nine is not a prime number, a whirring sound of 4000/60xc3x973 (Hz), attributed to a divisor of 3 for 9, is also generated.
The whirring sound becomes noise when the electronic equipment is in use, and a user may be uncomfortable with such noise. There is a need for a fan having low whirring sound level.
It is an object of the present invention to provide an axial fan and a centrifugal fan, featuring at least low-noise characteristics with low whirring sound level, and electronic equipment employing these fans.
An axial fan according to various exemplary embodiments of the present invention introduces the layout diversity of the blades, thereby lowering the level of whirring sound. The whirring sound would be high if a plurality of equally spaced blades were rotated. Specifically, the following methods are implemented.
An axial fan of an exemplary embodiment of the present invention includes a plurality of blades arranged around a rotation axis at a predetermined layout pitch. The plurality of the blades are rotated about the rotation axis to take in air in the direction of the rotation axis and to discharge the air. Some of the plurality of the blades are different from the remaining blades in shape thereof projected onto a plane perpendicular to the rotation axis.
Here, the clause xe2x80x9csome of the plurality of the blades are different from the remaining blades in the shape thereof projected onto a plane perpendicular to the rotation axisxe2x80x9d means that the width dimension of some blades is different from the width dimension of the remaining blades if viewed in the direction of the rotation axis. The shape of some blades is made different from the shape of the remaining blades by expanding an opening angle of the blades with respect to the rotation axis or by reducing a bending angle of the blade.
Since some of the plurality of the blades are different from the remaining blades in the shape thereof projected onto a plane perpendicular to the rotation axis in this exemplary embodiment, the layout diversity around the rotation axis is introduced. The whirring sound may be lower in level, compared with that which is caused by the blades having the same shape and arranged at an equal pitch. A low-noise axial fan may thus result.
An axial fan according to another exemplary embodiment of the present invention includes a plurality of blades arranged around a rotation axis at a predetermined layout pitch. The plurality of the blades are rotated about the rotation axis to take in air in the direction of the rotation axis and to discharge the air. Some of the plurality of the blades are different from the remaining blades in the cross-sectional shape taken in a plane in which the rotation axis lies.
The clause xe2x80x9csome of the plurality of the blades are different from the remaining blades in the cross-sectional shape taken in a plane in which the rotation axis liesxe2x80x9d means that the cross-sectional shape of some blades is made different from that of the remaining blades by setting some blades to be greater or smaller than the remaining blades in the angle of each blade made between a plane perpendicular to the rotation axis and a cross-sectional shape of the blade.
Since some of the plurality of the blades are different from the remaining blades in the cross-sectional shape, the layout diversity around the rotation axis is introduced in the same manner as in the previous embodiment. The whirring sound may thus be lower in level, compared with that which is caused by the blades having the same shape and arranged at an equal pitch. A low-noise axial fan may thus result.
An axial fan according to another exemplary embodiment of the present invention includes a plurality of blades arranged around a rotation axis at a predetermined layout pitch. The plurality of the blades are rotated about the rotation axis to take in air in the direction of the rotation axis and to discharge the air. Some of the plurality of the blades are different from the remaining blades in the layout pitch thereof.
The clause xe2x80x9csome of the plurality of the blades are different from the remaining blades in the layout pitch thereofxe2x80x9d means that, for instance, some of the nine blades are arranged around the rotation axis at a pitch of 30xc2x0 or 50xc2x0, while the remaining blades are arranged on the rotation axis at a pitch of 40xc2x0 degrees.
Since some of the plurality of the blades are different from the remaining blades in the layout pitch in this exemplary embodiment, the whirring sound may thus be lower in level, compared with that which is caused by the blades having the same shape and arranged at an equal pitch. A low-noise axial fan may thus result.
In this exemplary embodiment, from among the plurality of the blades, a pair of blades arranged to be generally diametrically symmetrical with respect to the rotation axis preferably have substantially the same layout pitch.
Specifically, if a first blade is changed in the layout pitch thereof in a nine-blade axial fan, a fifth blade, which is diametrically oppositely arranged across the rotation axis, is also equally changed in the layout pitch thereof.
Without greatly impairing the weight balance around the rotation axis of the axial fan, this arrangement may prevent clattering noise from being generated by the eccentricity of the axial fan during the rotation of a drive motor, thereby relieving a large load on the drive motor.
In the above-described exemplary embodiments, the number of the plurality of the blades is preferably a prime number.
Specifically, if the number of blades of an axial fan is 8 or 9, which is divisible by divisors 2 and 3 or 4, the whirring sound attributed to the divisors 2 and 3 or 4 is generated in addition to the whirring sound of the number of the blades. With the number of the blades of the fan set to a prime number, the whirring sound attributed to the divisors may be prevented. The low-noise characteristic of the axial fan may be even more enhanced.
In the above-described exemplary embodiments, the axial fan preferably includes an eccentricity adjusting device for adjusting weight balance around the rotation axis.
The eccentricity adjusting device can be formed by symmetrically arranging weights diametrically opposite with respect to the rotation axis where blades varied in planar shape, cross-sectional shape, or layout pitch are mounted. Specifically, the axial fan, formed of a plastic mold, includes a plurality of blades and a blade support member rotatably supported about the rotation axis. A projection or a notch is formed on the blade support member at the symmetrical positions diametrically opposite with respect to the rotation axis where the blades having different planar shapes are mounted. The weight balance is thus assured to compensate for the varied blades.
The axial fan thus has the eccentricity adjusting device. Even if some blades are varied in planar shape, cross-sectional shape, or layout pitch, the eccentricity adjusting device may assure the weight balance of the plurality of the blades and the blade support member around the rotation axis, thereby preventing a load from acting on the drive motor.
The above-referenced inventions are implemented not only in the axial fan but also in the centrifugal fan. The same operation and advantages will be enjoyed even if the above-referenced inventions are implemented in the centrifugal fan. The centrifugal fan refers to the one which includes a plurality of blades, arranged around a rotation axis at a predetermined layout pitch, wherein air is taken in the direction of the rotation axis and discharged in a direction tangential to the rotation of the plurality of the blades, by rotating the plurality of the blades around the rotation axis. For instance, a Sirocco fan is a centrifugal fan.
Since the centrifugal fan discharges air in the direction tangential to the rotation, discharged air pressure is large for a low rotational speed, compared with the axial fan. With the above inventions implemented, the whirring sound level may be lowered, and the low-noise characteristic of the centrifugal fan may be enhanced.
With one of the axial fan and the centrifugal fan discussed above incorporated in a personal computer or a projector, sound noise involved in the rotation of the fan during use is lowered in level, and low-noise electronic equipment thus results.